This invention is generally directed to toner compositions, and more specifically, the present invention is direct to developer and toner compositions, including magnetic toner compositons with inner salt charge enhancing additives, which additives impart a positive charge to the toner resin particles. Developer compositions containing the inner salt charge enhancing additives of the present invention are useful for enabling the development of electrostatic latent images including color images. More specifically, positively charged toner compositions comprised of the inner salt additives are particularly useful in electrostatographic imaging processes having incorporated therein a Viton coated fuser roll primarily since the inner salts do not react substantially with Viton causing undesirable decomposition thereof which adversely effects image quality. Also, the toner compositions of the present invention possess a high positive charge to mass ratio and narrow charge distributions.
Developer compositions with charge enhancing additives, especially additives which impart a positive charge to the toner resin, are well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of certain quanternary ammonium salts as charge control agents for electrostatic toner compositions. In accordance with the disclosure of this patent, certain quaternary ammonium salts when incorporated into a toner material provided a composition which exhibited relatively high uniform stable net toner charge when mixed with a suitable carrier vehicle. There is also described in U.S. Pat. Nos. 2,986,521 reversible developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica.
Also, there is disclosed in U.S. Pat. No. 4,338,390, the disclosure of which it totally incorporated herein by reference, developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate compositions. Other patents disclosing toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014; 4,396,697; 4,291,112; 4,415,646; and 4,394,430. Moreover, there is disclosed in U.S. Pat. No. 4,560,635, the disclosure of which is totally incorporated herein by reference, Viton compatible toner compositions containing therein as charge enhancing additives distearyl dimethyl ammonium methyl sulfate.
Further, there is illustrated in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions containing resin particles and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds and their hydrates of the formula as recited in column 3, beginning at line 14. Examples of alkyl pyridinium compounds disclosed included cetyl pyridinium chloride. While the developer compositions disclosed in the `672 patent are sufficient for their intended purposes, it appears that they react with the polymer contained on Viton fuser rolls causing decomposition thereof. Also, several of the other charge control agents disclosed in the prior art interact with certain fuser rolls, such as Viton fuser rolls used in electrostatographic systems. This interaction causes the fuser to be adversely effected resulting in deterioration of the image quality. For example, Viton fuser rolls discolor and turn black, develop multiple surface cracks and harden when certain charge control additive compounds are contained in the toner mixture.
One Viton fuser roll selected for use in electrostatographic copying machines is comprised of a soft roll fabricated from lead oxide, and duPont Viton E-430 resin, a vinyldene fluoride hexafluoropropylene copolymer. This roll contains approximately 15 parts of lead oxide, and 100 parts of Viton E-430, which mixture is blended and cured on the roll substrate at elevated temperatures. Apparently, the function of the lead oxide is to generate unsaturation by dehydrofluorination for crosslinking, and to provide release mechanisms for the toner composition. Excellent image quality has been obtained with Viton fuser rolls, however, in some instances there results a toner fuser compatibility problem when charge control agents are part of the toner mixture. For example, it appears that certain specific charge control additives, such as quaternary ammonium compounds and alkyl pyridinium compounds, including cetyl pyridinium chloride, react with the Viton of the Viton fuser roll. For example, cetyl pyridinium chloride when part of the toner mixture appears to be catalytically decomposed by the lead oxide contained in the fuser roll, resulting in a highly unsaturated compound, which polymerizes and condenses with the unsaturated Viton E-430 material. In view of this, the Viton fuser roll turns black, develops multiple surface cracks, and the surface thereof hardens thereby resulting in image quality deterioration.
Toner compositions comprised of many of the above described charge enhancing additives are useful for permitting the development of images formed on layered photoresponsive imaging devices comprised of generating layers and transport layers. These devices usually are charged negatively rather than positively as is the usual situation with selenium photoreceptors thereby requiring a toner composition that is positively charged in order that the toner particles may be suitably attracted to the electrostatic latent image contained on the photoreceptor surface. In view of this, extensive efforts have been devoted to obtaining developer compositions containing toner resins which are positively charged. Thus, while many charge control additives are known, there continues to be a need for new additives. Specifically, there continues to be a need for additives which will not substantially adversely interact with Vitonn type fuser rolls. Additionally, there continues to be a need for charge control additives which are thermally stable at high temperatures. Moreover, there continues to be a need for positively charged toner and developer compositions with acceptable humidity insensitivity since it is known that moisture contained in the atmosphere, or moisture from other sources can adversely effect the electrical properties of the toner compositions involved.
Also, there continues to be a need for new charge enhancing additives, particularly those additives where the negative charge center is covalently attached to the positive charge center, unlike the charge additives of the prior art with a cationic and anionic moiety. Additionally, there is a need for additives which in addition to being thermally stable are substantially nontoxic. Further, there is a need for toner compositions which contain positively charged resin particles, and wherein the resulting toner compositions have desirable toner admix charging characteristics. Also, there is a need for toner compositions with a high positive charge to mass ratio, and narrow charge distribution. Moreover, there is a need for toner compositions with charge enhancing additives wherein there is substantially no adverse impact on the minimum fusing temperature of the aforementioned composition, and further wherein the triboelectric charging properties of the resulting toner compositions are relatively stable for substantial time periods.